Photo-Conductive Semiconductor Switches (PCSS) have become important in high-speed optoelectronics and the generation and reshaping of ultrafast, high power electromagnetic pulses. PCSS are able to switch tens of kilovolts in sub-nanoseconds resulting in extremely high peak powers and are significantly advantageous over other voltage switches in easy fabrication, zero device-to-device jitter for multiple elements, and complete electrical isolation of the trigger.
PCSS are mostly based on either diode structure or bulk semiconductor. The diode-based PCSS, more specifically, P-i-N, consists of low doping semiconductor of high resistivity as the starting materials, and then P-type and N-type impurities are introduced on both sides to P-i-N doping profile. FIG. 1 and FIG. 2 illustrates cross sectional views of a diode-based PCSS 100. The PCSS 100 includes doped regions 102, 101 and 104 with junctions 103, 105 and 107, metallic electrodes (or terminals) 106 and 108, an optical aperture 107 on one of the electrodes and a single bevel profile 109 around the peripheral. The voltage holding is accomplished through the un-doped drift T region from the junction 103 near P-type region 102 and only in reverse bias. That is, diode-based PCSS 100 can only have one blocking polarity.
For certain circuit implementation, PCSS with dual blocking polarity are desired to simplify the circuit layout and reduce the number of component types. Bulk-type PCSS use lightly doped bulk semiconductor of high resistivity, and often additional doping of the same type is added near one or two electrodes, such as N-i-N type PCSS. The bulk-type PCSS is symmetric and can hold voltage in both polarities in general. However, the leakage current of bulk-type PCSS depends on the resistivity of starting material and is typically larger compared to those with junctions.
A need, therefore, exists for a new PCSS that can operate in dual polarities of voltage blocking and of less leakage. Also new PCSS should improve the stability of the devices while keeping the same form-factor as its diode-based counterparts without complicate bevels for edge termination.